Method of transferring a developed solid particulate image



H. H. HUNTER Feb. 4, 1964 METHOD OF TRANSFERRING A DEVELOPED SOLIDPARTICULATE IMAGE Filed Feb. 1, 1961 INVENTOR HARVEY H. HUNTER 15 A 7'TORNE V United States Patent Ofitice 3,2l2%,44t3 Feb. 4 1%4 l, No.85,524 :Cl. ill-17.5)

Thi invention relates to Xerography, and more par ticularly to thetrans-iv of Xerographic image ln a; or" Xerog a 1y it is conventional toform an electrostatic latent age on a Xerographic plate ineluding aphotocon uc ve insulating layer and to develop the latent image onxerographic plate by the selective electrostatic attraction thereto ofsuitable finely divided particles. Some development techniques, known tothe art and in commercial use, which share the common characteristicthat he particles and applied in a dry condi n, involve divided powdermaterials either by themselves or in conjunction with other particles.Another form of Xerographic development is known as liquid ismdevelopment and is accomplished by irnrnersi r image bearing member in asuspension of linel marking al suspended in a volatile insulat w ,uid.This develo c tent method is particularly tive for many applications,since it involves Ol tively si apparatus and since it h of developing ofextremely hag" resolution with a minimum of apparent iness.

In most, 'lthough not all ns of Xerography, it is desired to transferthe eveloper powder pattern from the Xerographic plate to some othermore suitable support member, such as a sheet of paper. arious methodsof accomplishing image transfer are known and include the use ofspecially coated papers or the like which have adhesive propertiestoward powder image, the use of electrostatic holds to transfer thepowder pattern, and the like. These transfer procedures are uiteol'lective when used with images produced by conventional drydevelopment processes nd such transfer methods enjoy wide commercialuse. It been found, however, that these methods applied to imagesproduced by liquid immersion development effect only incomplete transferresult. :1 images which are low in density, blotchy in appearance and oflow resolution. The reasons for such low on transier are rally l nown,but it is believed that the dry development methods deposit on theXerographic plate particles which are effectively surrounded by a thinair film and thus are readily removable from the plate. ln liquidimmersion development, however, the liquid of the developer evapo ratesas t e plate is w thdrawn from the developer, appar ently causing the p?11d cles to adhere to one another to the plate in a very intimatemanner. In addition, it is both possible and advantageous to useunusually fine developer particles in the liquid immersion process, andthese tend to adhere more tenaciously to a Xerographic plate than thesomewhat larger particles generally used in dry developing processes.

Now, in accordance with the present invention, there is provided animproved method for transferring images. The novel method or" transferof this invention is particularly applicable to developed images formedby a liquid process, and it is accordingly a principal objective of thepresent invention to provide improved Xerographic transfer methods totransfer liquid developed images. Also, in accordance with the presentinvention, there is provided an improved method of producing more conplete transfers than has heretofore been possible when transferringimages developed using, dry development techniques. Accordingly it is afurther objective of this invention to define novel and improvedtransfer methods for dry developed images. These, as well as subsidiaryobjectives, will become apparent from the following specification andfrom the drawing which represents a partially schematic view of magetransfer being carried out accordin to the invention.

The starting point of a Xerographic process is generally the formationof an electrostatic latent image. Methods are known whereby such imagesmay be formed on ordinary insulatins materials, and such images may beutilized in conjunction with the present invention. A more commonXerographic method involves the use of a Xerographic plate including aphotoconductive insulati layer as the latent image bearing member. Thephotoconductive insulating material may comprise a vit ous material,such as vitreous selenium, which may onal y be formed on a conductive orother support Other forms of photoconductive insulating mate- 13 areincluding dispersions of photoconductive as zinc oxide in an insulatingresin binder. h layers may also be formed on suitable supports which nDepending upon e nature of the photoconductor and 'ograpnic plates maybe either rigid or flexible. if ri d, they may be in the form of flatplates, cylir crs or other sh pes, and ii" flexible, they may be in theform of she webs or the like. The present plate in of these forms.

be formed on a e by uniiorr ly electrostatically charging g layer by anyof the known then selectively dissipating charge oy exposing theXerographic plate to a pattern or l ht and shadow as The latent electrosage may be developed or made visible by numerous methods, but sincetransfer according to the present invention is particularly valuable inconnection with n ersion method 0 developrne 0 g the latent image emploiliquid immersion development will be describe However, it is to berecalled that tlr principles of transfer are also applicable to an ima edeveloped g dry evelopment tech .iques, and it is intended to encompasssuch transfers within the scope of thi invei ion. In all applicationsthe liquid employed should, of course, not be a solvent for thedeveloped image.

In order to accomplish liquid development, the Xerographic plate bearingthe la.ent image is immersed in rwise contacted wi h a liquid developermaterial comprising a dispersion of finely ided particles in a liquidcarrier. The carrier liquid must be a hi hly insu lating material inorder to avoid discharge of the electrostatic latent image.Additionally, it should not be excessively viscous and should b; atleast moderately volatile, since the desired result of the developmentprocess is a dry image. This is most readily achieved by allowing theliquid to evaporate from a developed image leaving only the dryparticles behind. Many different liquids are suitable for use as carrierliquids in liquid develop- A particularly useful class of materialscomprises refined petroleum hydrocarbons having a volatility at leastabout as great as hat of kerosene, and preferably not more than aboutthat of gasoline. Such materials -y or may not be highly electricallyconductive.

invention operates with a A latent electrostatic nic o a technique ofdevelmay be employed as the solid component of the developer mixture.One useful class of materials comprises finely divided mineral pigmentsincluding fine metallic powders. Another useful class of materialscomprises pigmented or unpigmented resin particles similar to tonerswhich are widely used in conventional xerographic practice. Theseresinous materials may be ground to a fine particle size, or, whereparticularly fine particles are desired, they may be formed by spraydrying a solvent solution of the resin material. In general, particlesused in liquid development have a particle size of a few microns atmost. When dispersed in the carrier liquid, the particles acquire eitherpositive or negative electrostatic charge, depending upon the particularchoice of powder and liquid materials. In accordance with conventionalxerographic principles, a powder having a polarity, when mixed in thecarrier liquid, opposite to that of the latent image pattern is employedwhen it is desired to develop the charged areas of the latent image andparticles of like polarity, when mixed in the carrier liquid, areselected when unchanged area development is desired. A further componentin the form of a soluble film forming materials, such as linseed oil, issometimes included in the developer mixture to increase the permanenceof the developed image. For general information on liquid development,reference may be had to British Patent 755,486, US. Patent 2,899,335 andUS. Patent 2,913,353.

In carrying out the present invention the first step is the formation ofan electrostatic latent image. This is generally carried out byelectrostatically charging a xerographic plate and exposing it to apattern of light and shadow. The latent image is then developed byimmersing or otherwise wetting it with a liquid developer material ofthe type already described. In accordance with conventional techniques,the xerographic plate would then be removed from the developer materialand evaporation of the carrier liquid would soon leave a dry powderimage on the plate. Such an image is useful for many purposes but, asalready pointed out, cannot be readily transferred to a further support.

In accordance with an improved form of transfer, however, and asillustrated in the drawnig, the developed xerographic plate isreimmersed into the liquid carrier of the developer dispersion and whileso immersed is contacted with a sheet of paper or other transfer member.In the drawing, there is shown a tray which is partly filled withcarrier liquid 11 and is which is immersed a xerographic plate 12including a photoconductive insulating layer 13 overlying a supportlayer 14. A transfer member 15 such as paper or the like is shown beingrolled into contact with plate 12 by a roller 16. Roller 16 includes aninsulating handle 17 and a conductive rubber cylindrical element 18overlying a conductive core 9. The operative portion of the roller 16 ismaintained at a potential in the range of from 1,000 to 3,000 volts DC.through a connection to a power supply 19. The support layer 14 of plate12 is simultaneously maintained at zero potential through its contactwith tray 10 which in this embodiment is both electrically conductiveand electrically grounded. The electrical field established betweenpaper 15 and plate 12 causes the developer particles on plate 12 totransfer to paper 15. Since these developer particles are wetted by theliquid of carrier liquid 11, they are not tightly bonded to plate 12except by electrostatic forces which are readily overcome by thepotential applied to roller 16. After roller 16 has passed over paper15, the paper may be separated from plate 12 and upon evaporation of thecarrier liquid from the paper, there is formed a dry developed image onthe paper. It is desirable, but not essential, to maintain an imagebearing plate in darkness through the transfer process, and this isparticularly so when transferring following uncharged area typedevelopment. Of course, if the image bearing member is not lightsensitive, precautions need not be taken against exposure to light.

A particularly useful roller 16, used in connection with the abovemethod and the improved methods of the present invention, included anelectrically conductive silicone rubber cylindrical element 2 inches indiameter over a l-inch diameter metal core. The roll had a durometerhardness of 42 and the electrical resistance was of the order of 10 ohmsfor a 6-inch long member measured between the metal core and a fiatmetal plate in contact with the outside of the roll while the roll wasunder an applied force of 10 pounds.

The figure represents only a specific embodiment of image transfer withrespect to both methods and material. Thus, transfer member 15 isgenerally representative of a class of transfer materials which arecharacterized as having at least an insulating surface or substantiallyinsulating surface. Ordinary paper is sufficiently insulating for usewith this transfer method. In addition to ordinary paper, one can employeither paper or metals coated with insulating plastics or the like. Suchcoatings are chosen to be insoluble in the carrier liquid to avoid imagedeterioration which otherwise results. The transfer material should alsohave a smooth surface to permit intimate contact with the surface ofplate 12. A particularly suitable paper has been found to be Kromekotecast-coated paper manufactured by the Champion Paper and Fiber Company,Hamilton, Ohio. Sheets of Mylar polyester film have also been usedsuccessfully. While plate 12 is shown as being immersed in the developertray, it is only necessary in carrying out this transfer method that thedeveloped image and area of its contact with the plate be wet, and thus,transfer may, for example, be effected outside of the developer afterwetting the image and before the liquid has evaporated.

The illustrated and described conductive rubber roller in conjunctionwith a conductive tray is merely one way in which intimate contact canbe established between transfer member 15 and plate 12 whileestablishing a strong electric field between them. Other forms ofrollers or even flat, conductive plates may be substituted for roller16, and a variety of means may be used to maintain support layer 14 at adifferent potential from that of roller 16 or its equivalent. Inaccordance with conventional xerographic practice, transfer can also beeffected by passing a corona charging device adjacent to paper 15 whileit is in contact with plate 12. This can be accomplished while plate 12is moist, but cannot readily be carried out where the plate and transfermember are actually immersed beneath the surface of a liquid bath at thetime of transfer.

Particle transfer from the xerographic plate to the transfer material iscarried out in the foregoing procedure through the agency of an electricfield which is maintained between the plate and transfer materialthrough potentials applied to external rollers, electrodes, or the like.It is, however, also possible to effect transfer in accordance with thepresent invention by electric fields generated internally of theplate-transfer member combination rather than externally thereof. Inaccordance with this further embodiment, the developed xerographic plateis removed from the developer bath and is uniformly electrostaticallycharged. Such charging may be performed by any conventional form ofcorona charging apparatus or the like, but is most convenientlyper-formed in the same apparatus previously used to charge the plate inconnection with the described process of electrostatic latent imageformation. The potential to which the plate and the image thereon arecharged is not critical and may be on the order of several hundredvolts. Since this is the same range of potentials generally used inconnection with charging a plate for image formation, the same chargingapparatus as previously used may be employed for this second chargingwithout any readjustment thereof. The plate is then contactedwith asheet of paper or other transfer material in the same general manner asdescribed above and shown in the drawing. If the plate bearing thedeveloped image Was wetted prior to this charging operation transfer maybe carried out without further wetting. However, if the surface of theXerographic plate is not very wet appearing, it may be desirable toreiminerse the plate and transfer member in a bath of dielectric liquid.With this embodiment it is however, not necessary to apply a potentialto roller 16 from power supply 19, and it is instead only required thatthe xerographic plate and the transfer material be brought into contactand that the backs or outer surfaces of the plate and paper or othertransfer member be brought to about the same electrical potential. Thismay conveniently be accomplished by the same apparatus shown in thedrawing. In this embodiment the developer particles are transferred fromthe plate to the paper by the electric fields resulting from the uniformcharge layer previously deposited on the Xerographic plate. It is alsopermissible to apply a potential to roller 16 or to deposit uniformcharge on the outer surface of the transfer member as through the use ofa corona discharge electrode or the like in connection with thisembodiment of the invention. It has been found that slightly superior orslightly inferior results are obtained with the added roller potential,depending upon the particular developer materials em ployed, thepotential applied and the like. Best results to date in connection withthis invention have resulted following chargin of the developed plateand then immersed transfer employing a grounded roller.

The invention has thus far been described in terms of a developed imageformed using liquid immersion developing techniques. All embodimentsdiscussed, however, have been employed starting with an image developedusing dry development techniques such as cascade, powder cloud and thelike. In such cases it is found that more complete transfers result whencompared to dry transfer techniques.

The above procedures have been found to create transferred images ofhigh density, a high degree of uniformity and very high resolution whenused with a wide variety of Xerographic plates, carrier liquids andpowder materials. There is, however, a tendency with the above methodsto deposit background, i.e., a uniform deposition of powder, in additionto the powder corresponding to the electrostatic latent image if thecarrier liquid becomes dirty with developer particles. This backgroundproblem can be avoided or overcome by refreshing the carrier liquid orby using a clean batch free of developer particles. Since a cleancarrier bath is free of particles, the only particles which transfer arethose particles electrostatically adherent on the Xero-graphic plate,and there results a background-free transferred image.

a .e invention has been described in terms of certain physical forms ofapparatus, but it is to be understood that such description was forillustrative purposes only rather than by Way of limitation. Transferaccording to the present invention may be carried out with various formsof development apparatus, various forms of Xerographic plates, variousmeans for contacting the xerographic plate with the transfer materialand various means for applying electric fields therebetween. While theinvention has been described in terms of a manual operation, it isapparent that it can be adapted to various forms of automatic processingequipment. These and various other modifications lie within the scope ofthe invention and are intended to be encompassed within the appendedclaims.

What is claimed is:

l. The method of transferring a developed solid particulate image froman image bearing surface comprising contacting the developed image andthe image bearing surface with a developer-free, electrically insulatingiquid incapable of dissolving said image, positioning a transfer webacross the developed image and image bearing surface while said imagecontinues to be Wet with said insulating liquid, and applyingelectrostatic field between said developed image and said transfer webto cause movement of said still wet developed image to said transferWeb.

2. The method of claim 1 in which said electrostatic field is applied byrolling a roller at a raised potential across the rear surface of saidtransfer web.

3. The method of claim 1 in which said electrostatic field is applied bydepositing charge on the rear surface of said transfer web from a coronadischarge electrode.

4-. The method of claim 1 in which the developed image comprises a drydeveloped image.

5. The method of claim 4 in which said dry developed image is developedemploying a dry development techni ue.

6. The method of claim 1 in which said electrostatic field is applied byfirst corona chargin the image bearing surface prior to positioning thetransfer Web across the image bearing surface and then applying auniform electrostatic potential across the rear surface of said tra sferweb while said transfer web is across said image bear' surface.

7. The method of claim 6 in which said uniform electrostatic potentialis applied across said transfer web by corona discharge.

8. The method of claim 6 in which said uniform electrostatic potentialis applied across said transfer web by a contacting electrode at a biaspotential.

9. The method of transferring a developed solid particulate image froman image bearing surface to a transfer Web comprising contacting thedeveloped particulate image and the image bearing surface with a pattilofree, volatile, electrically insulating liquid in which said imag saidsurface and said web are each insoluble, positioning a transfer webacross the developed image and irnage bearing surface while said imagecontinues to be wet with said insulating liquid, appling anelectrostatic field between said developed image and said transfer webto cause movement of said still wet developed image to said transferWeb, then separating said transfer Web from said image bearing surfacewith said transfer web bearing said developed image, and allowing saidvolatile liquid to evaporate from the transferred developed image.

10. The method of transferring a developed particulate image from asurface hearing such image comprising wetting the developed image andthe image bearing surface with a p: ticle-free, electrically insulatingliquid incapable of dissolving said image, uniformly electro staticallycharging said image and image bearing surface while said image andsurface remain in a Wet condition, positioning a transfer web having aninsulating surface across the developed image on said image bearingsurface while said image and said surface continue to be wet with saidinsulating liquid, and separating said transfer web from said imagebearing surface with said transfer web bea 'ng said developed image.

11. The method of claim it) including applying a grounded roller againstthe back surface of said transfer web prior to separating said transferweb from said image bearing surface.

12. The method of claim 10 including applying a uniform electrostaticpotential from a corona discharge electrode to the back surface of saidtransfer web prior to separating said transfer Web from said imagebearing surface.

13. in an image reproducing process wherein an electrostatic image bearng surface is developed by the selective electrostatic depositionthereon in image configuration of a pattern of finely divided solidparticles from a suspension of said particl s in a volatile,electrically insulating liquid, the improvement comprising removing thedeveloped image bearing surface from said suspension into a bath ofvolatile, particle-free, electrically insulating liquid incapable ofdissolving said particles, and electrostatically transferring saidpattern of finely divided particles to a contacting transfer sheet whileat least the image bearing member is wet by said volatile particle-freeinsulating liquid.

'14. The improvement in the process of claim 13 including using the sameelectrically insulating liquid as employed in the suspension ofparticles as the volatile insulating liquid in the both of volatileparticle-free insulating liquid.

15. In an image reproducing process wherein an electrostatic imagebearing surface is developed by the selective electrostatic depositionthereon in image configuration of a pattern of finely divided particlesfrom a suspension of said particles in a volatile insulating liquid, theimprovement comprising removing the image bearing suriace from saidsuspension to a bath of volatile, particlefree, electrically insulatingliquid incapable of dissolving said particles, while maintaining theimage bearing surface in a moistened condition contacting said patternof finely divided particles on the image bearing surface with a transfermaterial including at least an insulating layer facing the image'bearingmember, establishing an electric field between the image bearing memberand the transfer material While at least the image bearing member is wetby said insulating liquid, and separating the transfer member from theimage bearing member.

References Cited in the file of this patent UNITED STATES PATENTS2,551,582 Carlson May 8, 1951 2,940,847 Kaprelian June 14, 19602,951,443 Byrne Sept. 6, 1960 2,959,153 Hider Nov. 8, 1960 UNITED STATESPATENT OFFICE CERTIFICATE OF CORRECTION Patent New 3 IQO IMJ February 411964 I Harvey HO Hunter It is hereby certified that error appears in theabove numbered natent requiring correction and that the said LettersPatent should read as corrected below.

Column 3 line .20 for "unchanged" read uncharged eolumn 7 line 6 for"both" read bath Signed and sealed this 8th day of September I964 (SEAL)Attest:

ERNEST W. SWIDER' EDWARD J. BRENNER Attesting Officer Commissioner ofPatents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N093 120 446 February 4L 1964 Harvey H Hunter It is hereby certified, thaterror appears in the above numbered batent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 3 line 2O for "unchanged" read uncharged column 7 line 6 for"both" read bath Signed and sealed this 8th day of September 1964.,

(SEAL) Attest:

ERNEST W. SWIDER' EDWARD J. BRENNER Attesting Officer Commissioner ofPatents

1. THE METHOD OF TRANSFERRING A DEVELPED SOLID PARTICULATE IMAGE FROM ANIMAGE BEARING SURFACE COMPRISING CONTACTING THE DEVELOPED IMAGE AND THEIMAGE BEARING SURFACE WITH A DEVELOPER-FREE, ELECTRICALLY INSULATINGLIQUID INCAPABLE OF DISSOLVING SAID IMAGE, POSITIONING A TRANSFER WEBACROSS THE DEVELOPED IMAGE AND IMAGE BEARING SURFACE WHILE SAID IMAGECONTINUES TO BE WET WITH SAID INSULATING LIQUID, AND APPLYING ANELECTROSTATIC FIELD BETWEEN SAID DEVELOPED IMAGE AND SAID TRANSFER WEBTO CAUSE MOVEMENT OF SAID STILL WET DEVELOPED IMAGE TO SAID TRANSFERWEB.
 4. THE METHOD OF CLAIM 1 IN WHICH THE DEVELOPED IMAGE COMPRISES ADRY DEVELOPED IMAGE.